I honestly don't think there should be big/intense firefights commonly in Tarkov.
Lets be honest, if you are running M61 and mag-dumping, you are not playing to the ideals of the game. This is a game that SHOULD reward taking firefights where you cannot possibly lose. If I am at risk of even losing a fire fight, then I should not risk it, realistically. Your goal should be to end each fire fight as soon as possible.
To that end, the ideal firefight is at a range where to shooter does not give the victim a chance to even respond. Imagine a 100m+ headshot or similar. This can be countered by rushing the shooter, but you would obviously risk your life in that method.
TTK SHOULD BE LOW. Bullets hurt, and getting shot anywhere in the body will knock you on your ass (with a decent caliber).
Here are some interesting links:
The current US military offers the IOTV as their premier frontline body armor. It natively protects somewhat from 9mm bullets. It also allows for inserts of Type III and Type IV armor.
Type III armor (in the wiki) is able to protect from A SINGLE 7.62 x 39mm BULLET. The more formal PDF I also linked says that it can be defeated (i.e. destroyed/shredded ) by ~6 rounds. I would argue that 3-4 bullets COULD be stopped by Type III armor, in an ideal scenario.
Type IV armor (in the wiki) can stop some rounds of .30-06 AP rounds, which based on my research is an older round from WWII. (
So, in my opinion, TTK should be low. It should be <1 second. Frankly, it should be <.5 seconds ideally. If you can hit 3-4 shots on a torso sized object from 25-50 yards meters, you should be able to kill that person, assuming that you are running the appropriate ammo.
If you want to feel tanky and indestructible, run at someone shooting their 1911, not someone shooting their big boy bullets.